Transformed liver cells have modified transplasma membrane redox activity which is sensitive to adriamycin

Characterization of Transplasma Membrane Electron Transport Chain in Wild and Drug-Resistant Leishmania donovani Promastigote and Amastigote

BACKGROUND

Leishmania donovani (L. donovani) is one of the parasites that cause leishmaniasis. The mechanisms by which L. donovani fights against adverse environment and becomes resistant to drugs are not well understood yet.

OBJECTIVE

The present study was designed to evaluate the effects of different regulators on the modulation of Transplasma Membrane Electron Transport (transPMET) systems of susceptible and resistant L. donovani cells.

MATERIALS AND METHODS

Effects of UV, different buffers, and electron transport inhibitors and stimulators on the reduction of α-lipoic acid (ALA), 1,2-naphthoquinone-4-sulphonic acid (NQSA) and ferricyanide were determined.

RESULTS AND DISCUSSION

ALA reductions were inhibited in susceptible, sodium antimony gluconate (SAG)-resistant and paromomycin (PMM)-resistant AG83 amastigote cells, and stimulated in susceptible and SAG-resistant AG83 promastigote cells upon UV exposure. The results indicate that UV irradiation almost oppositely affect ALA reductions in amastigotes and promastigotes. ALA reductions were stimulated in sensitive and inhibited in resistant GE1 amastigotes upon UV exposure. Susceptible amastigotes and promastigotes inhibited, and resistant amastigotes and promastigotes stimulated NQSA reduction under UV irradiation. Thus, susceptible and drug-resistant amastigotes and promastigotes are different in the reduction of ALA. Susceptible and resistant AG83 amastigotes and promastigotes inhibited the ferricyanide reductions upon UV exposure, which indicates, there is no such difference in ferricyanide reductions among susceptible as well as resistant AG83 amastigotes and promastigotes. The reductions of extracellular electron excerptors in susceptible promastigotes requires the availability of Na⁺ and Cl^- ions for maximal activity but susceptible amastigotes are mostly not dependent on the availability of Na⁺ and Cl^- ions. Both in promastigotes and amastigotes, reductions of electron acceptors were strongly inhibited by carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone. Furthermore, antimycin A, rotenone and capsaicin markedly inhibited the reductions of electron acceptors in promastigotes, but not in amastigotes.

CONCLUSION

Results of this study suggest that the transPMET system is functionally different in wild and resistant strains of L. donovani.

Characterization of the redox components of transplasma membrane electron transport system from Leishmania donovani promastigotes

An investigation has been made of the points of coupling of four nonpermeable electron acceptors e.g., alpha-lipoic acid (ALA), 5,5'-dithiobis (2-nitroaniline-N-sulphonic acid) (DTNS), 1,2-naphthoquinone-4-sulphonic acid (NQSA) and ferricyanide which are mainly reduced via an interaction with the redox sites present in the plasma membrane of Leishmania donovani promastigotes. ALA, DTNS, NQSA and ferricyanide reduction and part of O2 reduction is shown to take place on the exoplasmic face of the cell, for it is affected by external pH and agents that react with the external surface. Redox enzymes of the transplasma membrane electron transport system orderly transfer electron from one redox carrier to the next with the molecular oxygen as the final electron acceptor. The redox carriers mediate the transfer of electrons from metabolically generated reductant to nonpermeable electron acceptors and oxygen. At a pH of 6.4, respiration of Leishmania cells on glucose substrate shut down almost completely upon addition of an uncoupler FCCP and K+-ionophore valinomycin. The most pronounced effects on O2 uptake were obtained by treatment with antimycin A, 2-heptadecyl-4-hydroxyquinone-N-oxide, paracholoromercuribenzene sulphonic acid and trifluoperazine. Relatively smaller effects were obtained by treatment with potassium cyanide. Inhibition observed with respect to the reduction of the electron acceptors ALA, DTNS, NQSA and ferricyanide was not similar in most cases. The redox chain appears to be branched at several points and it is suggested that this redox chain incorporate iron-sulphur center, b-cytochromes, cyanide insensitive oxygen redox site, Na+ and K+ channel, capsaicin inhibited energy coupling site and trifluoperazine inhibited energy linked P-type ATPase. We analyzed the influence of ionic composition of the medium on reduction of electron acceptors in Leishmania donovani promastigotes. Our data suggest that K+ have some role for ALA reduction and Na+ for ferricyanide reduction. No significant effects were found with DTNS and NQSA reduction when Na+ or K+ was omitted from the medium. Stimulation of ALA, DTNS, NQSA and ferricyanide reduction was obtained by omitting Cl- from the medium. We propose that this redox system may be an energy source for control of membrane function in Leishmania cells.

Transplasma membrane electron transport in Leishmania donovani promastigotes

Leishmania donovani promastigotes are capable of reducing certain electron acceptors with redox potential at pH 7 down to -125 mV; outside the plasma membrane promastigotes can reduce ferricyanide. Ferricyanide has been used as an artificial electron acceptor probe for studying the mechanism of transplasma membrane electron transport. Transmembrane ferricyanide reduction by L. donovani promastigotes was not inhibited by such mitochondrial inhibitors as antimycin A or cyanide, but it responded to inhibitors of glycolysis. Transmembrane ferricyanide reduction by Leishmania appears to involve a plasma membrane electron transport chain dissimilar to that of hepatocyte cells. As with other cells, transmembrane electron transport is associated with proton release, which may be involved in internal pH regulation. The Leishmania transmembrane redox system differs from that of mammalian cells in being 4-fold less sensitive to chloroquine and 12-fold more sensitive to niclosamide. Sensitivities to these drugs suggest that transplasma membrane electron transport and associated proton pumping may be targets for the drugs used against leishmaniasis.

Evidence for the extracellular reduction of alpha-lipoic acid by Leishmania donovani promastigotes: a transplasma membrane redox system

Leishmania donovani cells, capable of reducing certain electron acceptors with redox potentials at pH 7.0 down to -290 mV, outside the plasma membrane, can reduce the oxidised form of alpha-lipoic acid. alpha-Lipoic acid has been used as natural electron acceptor probe for studying the mechanism of transplasma membrane electron transport. Transmembrane alpha-lipoic acid reduction by Leishmania was not inhibited by mitochondrial inhibitors as azide, cyanide, rotenone or antimycin A, but responded to hemin, modifiers of sulphhydryl groups and inhibitor of glycolysis. The protonophores carbonyl cyanide chlorophenylhydrazone and 2,4-dinitrophenol showed inhibition of alpha-lipoic acid reduction. This transmembrane redox system differs from that of mammalian cells in respect to its sensitivity of UV irradiation and stimulation by diphenylamine. Thus a naphthoquinone coenzyme appears to be involved in alpha-lipoic acid reduction by Leishmania cells.

Is the drug-responsive NADH oxidase of the cancer cell plasma membrane a molecular target for adriamycin?

Enhanced growth inhibition and antitumor responses to adriamycin have been observed repeatedly from several laboratories using impermeant forms of adriamycin where entry into the cell was greatly reduced or prevented. Our laboratory has described an NADH oxidase activity at the external surface of plasma membrane vesicles from tumor cells where inhibition by an antitumor sulfonylurea, N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984), and by the vanilloid, capsaicin (8-methyl-N-vanillyl-6-noneamide) correlated with inhibition of growth. Here we report that the oxidation of NADH by isolated plasma membrane vesicles was inhibited, as well, by adriamycin. An external site of inhibition was indicated from studies where impermeant adriamycin conjugates were used. The EC50 for inhibition of the oxidase of rat hepatoma plasma membranes by adriamycin was several orders of magnitude less than that for rat liver. Adriamycin cross-linked to diferric transferrin and other impermeant supports also was effective in inhibition of NADH oxidation by isolated plasma membrane vesicles and in inhibition of growth of cultured cells. The findings suggest the NADH oxidase of the plasma membrane as a growth-related adriamycin target at the surface of cancer cells responsive to adriamycin. Whereas DNA intercalation remains clearly one of the principal bases for the cytotoxic action of free adriamycin, this second site, possibly related to a more specific antitumor action, may be helpful in understanding the enhanced efficacy reported previously for immobilized adriamycin forms compared to free adriamycin.

The hepatotoxicity of rhein involves impairment of mitochondrial functions

Metabolism of rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid) in primary cultures of rat hepatocytes caused production of oxygen-derived free radicals by redox cycling; this was shown as an increased rate of superoxide-dismutasesensitive NAD(P)H oxidation and NAD(P)H-cytochrome c reduction. Furthermore, rhein caused a depletion of intracellular reduced glutathione and an immediate, almost 10-fold increase in intracellular free Ca2+. Exposure to rhein also induced the following: a decrease in the mitochondrial membrane potential, as analyzed by uptake of rhodamine 123 (Rh 123); initiation of lipid peroxidation, measured as accumulation of malondialdehyde and 4-hydroxyalkenals; and cell death (LD50 = 20 microM). Pretreatment of cell cultures with dithiothreitol (DTT), nifedipin or N',N'-diphenyl-p-phenylenediamine (DPPD) increased the intracellular free Ca2+ concentration 5-fold but inhibited rhein-induced cytotoxicity. Moreover, addition of these protecting substances maintained the level of ATP and glutathione (GSH) and prevented accumulation of lipid peroxidation products. Depletion of intracellular glutathione by pretreatment with buthionine sulfoximine (BSO), or inhibition of glutathione reductase with 1,3-bis-2-chloroethyl-1-nitrosourea (BCNU) decreased cell viability (LD50 = 2.5 microM). On the other hand, increasing GSH by pretreatment with L-2-oxothiazolidine-4-carboxylic acid (OTC) did not provide complete protection. In summary, rhein undergoes redox cycling that gives rise to oxygen metabolites that affect the mitochondrial membranes (recorded as a decreased membrane potential) and after the plasma membrane (i.e. induced the formation of surface blebs). Mitochondrial malfunction also causes changes in Ca2+ homeostasis and depletion of ATP, which eventually lead to cell death.

Ehrlich cell plasma membrane redox system is modulated through signal transduction pathways involving cGMP and Ca2+ as second messengers

Ehrlich cell plasma membrane ferricyanide reductase activity increased in the presence of mastoparan, a generic activator of G proteins, using either whole cells or isolated plasma membrane-fractions. Agents that increase intracellular cAMP also increased the rate of ferricyanide reduction by Ehrlich cells. For the first time, evidence is shown on a modulation of plasma membrane redox system by cGMP. In fact, permeant analogs of cGMP, dibutyryl cGMP, and 8-bromo-cGMP increased the rate of ferricyanide reduction by the Ehrlich cell plasma membrane redox system. Furthermore, specific inhibition of cGMP-phosphodiesterases by dipyridamole was also accompanied by an enhancement in the rate of ferricyanide reduction. On the other hand, treatments expected to increase cytoplasmic Ca2+ concentrations were accompanied by a remarkable stimulation of the reductase activity. Taking all these data together, it seems that the Ehrlich cell plasma membrane redox system is under a multiple and complex regulation by different signal transduction pathways involving G proteins, cyclic nucleotides, and Ca2+ ions.

Extracellular ferrireductase activity of K562 cells is coupled to transferrin-independent iron transport

The reduction of Fe3+ to Fe2+ has been established to play a critical role in the uptake of iron by many organisms. Recently, a mechanism of iron transport in the absence of transferrin (Tf) was described for the human K562 cell line and a role for ferrireductase activity was implicated in this process as well [Inman, R. S., & Wessling-Resnick, M. (1993) J. Biol. Chem. 268, 8521-8528]. The present report characterizes the extracellular reduction of ferricyanide to ferrocyanide catalyzed by K562 cells. The observation that membrane-impermeant ferricyanide competitively inhibits Tf-independent assimilation of iron from 55Fe-nitriloacetic acid indicates that this ferrireductase activity is indeed coupled to the transport mechanism. From a series of initial rate experiments, the kinetic parameters for cell surface ferrireductase activity, Vmax = 0.102 nmol min-1 (10(6) cells)-1 and Km = 6.13 microM, were determined. Neither the Vmax nor the Km of this reaction is modulated by changes in extra- or intracellular iron levels; thus, similar to Tf-independent transport activity in K562 cells, the ferrireductase activity is not regulated in response to iron levels. Transmembrane oxidoreductase activity is also reportedly involved in the control of cellular growth; however, the K562 cell ferrireductase is unresponsive to insulin and is not inhibited by the antitumor drugs adriamycin, actinomycin D, or cis-platin, observations that fail to support a role for this particular activity in cell regulation. Rather, the K562 cell ferrireductase appears to be tightly coupled to the mechanism of Tf-independent transport as demonstrated by its sensitivity to Cd2+, a specific inhibitor of non-Tf iron uptake by K562 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The changes of prooxidant and antioxidant enzyme activities in bovine leukemia virus-transformed cells. Their influence on quinone cytotoxicity

It was found that the activities of prooxidant enzymes (NAD(P)H oxidases and NAD(P)H:cytochrome c reductases) in bovine leukemia virus-transformed calf and lamb embryo kidney fibroblasts (lines Mi-18 and FLK) were by 1.25-18 times higher when compared to corresponding nontransformed calf cells. The activity of DT-diaphorase was also increased by about one order of magnitude in transformed cells. The activities of antioxidant enzymes were almost unchanged (superoxide dismutase), decreased by 13% or 53% (catalase) or increased by 25% or 90% (glutathione reductase) in Mi-18 or FLK cells, respectively. These changes of enzyme activity increased the toxicity of simple redox-cycling quinones (duroquinone, naphthazarin) towards transformed cells, but did not affect the toxicity of daunorubicin. The latter was most probably related to the inhibition of plasma membrane NADH dehydrogenase.

Epirubicin. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in cancer chemotherapy

Epirubicin is the 4' epimer of the anthracycline antibiotic doxorubicin, and has been used alone or in combination with other cytotoxic agents in the treatment of a variety of malignancies. Comparative and noncomparative clinical trials have demonstrated that regimens containing conventional doses of epirubicin achieved equivalent objective response rates and overall median survival as similar doxorubicin-containing regimens in the treatment of advanced and early breast cancer, non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC), non-Hodgkin's lymphoma, ovarian cancer, gastric cancer and nonresectable primary hepatocellular carcinoma. Recently, dose-intensive regimens of epirubicin have achieved high response rates in a number of malignancies including early and advanced breast cancer and lung cancer. The major acute dose-limiting toxicity of anthracyclines is myelosuppression. In vitro and clinical studies have shown that, at equimolar doses, epirubicin is less myelotoxic than doxorubicin. The lower haematological toxicity of epirubicin, as well as the recent introduction of supportive measures such as colony-stimulating factors, has allowed dose-intensification of epirubicin-containing regimens, which is particularly significant because of the definite dose-response relationship of anthracyclines. Cardiotoxicity, which is manifested clinically as irreversible congestive heart failure and/or cardiomyopathy, is the most important chronic cumulative dose-limiting toxicity of anthracyclines. Epirubicin has a lower propensity to produce cardiotoxic effects than doxorubicin, and its recommended maximum cumulative dose is almost double that of doxorubicin, thus allowing for more treatment cycles and/or higher doses of epirubicin. In summary, dose-intensive epirubicin-containing regimens, which are feasible due to its lower myelosuppression and cardiotoxicity, have produced high response rates in early breast cancer, a potentially curable malignancy, as well as advanced breast, and lung cancers. Furthermore, there is evidence to suggest that improved response rates can improve quality of life in some clinical settings, but whether this leads to prolonged survival has not yet been determined. Recently implemented supportive measures such as colony-stimulating factors, prophylactic antimicrobials and peripheral blood stem cell support may help achieve other potential advantages of dose-intensive epirubicin-containing regimens such as reductions in morbidity and length of hospital admissions.

Plasma membrane redox activity correlates with N-myc expression in neuroblastoma cells

In different neuroblastoma cell lines and transfected clones, an increasing plasma membrane redox activity correlates with amplification and enhanced expression of the N-myc oncogene. Furthermore, plasma membrane redox activity is partially inhibited by retinoic acid in neuroblastoma cells with multiple copies of the N-myc oncogene but not in neuroblastoma cells with only one copy of this gene.

Characterization of the anti-cancer activity of transferrin-adriamycin conjugates

The anthracycline anti-cancer drug adriamycin (Adr) was coupled to human transferrin (Trf) by using a glutaraldehyde technique. The effect of Trf-Adr conjugates and unconjugated Adr on human cells was determined by using normal peripheral blood mononuclear cells and chronic myelogenous K562 cells. Cytotoxicity was determined by using an assay that measures the conversion of a tetrazolium salt (MTT) into a purple product (formazan) by mitochondrial dehydrogenases in viable cells. We found that free Adr at a concentration of 1 x 10(-7) had little effect on K562 cells, while Trf-Adr conjugates inhibited 75% of cellular activity. When normal peripheral blood mononuclear cells were tested against Trf-Adr conjugates, the 50% inhibitory concentration was found to be 1.4-1.7 x 10(-6) M, at which concentration greater than 85% of K562 cells were inhibited. Interactions of Trf-Adr conjugates with plasma membrane energy-producing systems are the proposed mechanisms of cytotoxicity.

A growth factor- and hormone-stimulated NADH oxidase from rat liver plasma membrane

NADH oxidase activity (electron transfer from NADH to molecular oxygen) of plasma membranes purified from rat liver was characterized by a cyanide-insensitive rate of 1 to 5 nmol/min per mg protein. The activity was stimulated by growth factors (diferric transferrin and epidermal growth factor) and hormones (insulin and pituitary extract) 2- to 3-fold. In contrast, NADH oxidase was inhibited up to 80% by several agents known to inhibit growth or induce differentiation (retinoic acid, calcitriol, and the monosialoganglioside, GM3). The growth factor-responsive NADH oxidase of isolated plasma membranes was not inhibited by common inhibitors of oxidoreductases of endoplasmic reticulum or mitochondria. As well, NADH oxidase of the plasma membrane was stimulated by concentrations of detergents which strongly inhibited mitochondrial NADH oxidases and by lysolipids or fatty acids. Growth factor-responsive NADH oxidase, however, was inhibited greater than 90% by chloroquine and quinone analogues. Addition of coenzyme Q10 stimulated the activity and partially reversed the analogue inhibition. The pH optimum for NADH oxidase was 7.0 both in the absence and presence of growth factors. The Km for NADH was 5 microM and was increased in the presence of growth factors. The stoichiometry of the electron transfer reaction from NADH to oxygen was 2 to 1, indicating a 2 electron transfer. NADH oxidase was separated from NADH-ferricyanide reductase, also present at the plasma membrane, by ion exchange chromatography. Taken together, the evidence suggests that NADH oxidase of the plasma membrane is a unique oxidoreductase and may be important to the regulation of cell growth.

Intracellular actions of vitamin A

Because the effects of vitamin A vary with tissue type and often with the form of vitamin A itself, a complete understanding of the mechanism(s) of action still has not been attained. The action of vitamin A may be at the level of genomic expression, at the membrane level, or both. Intercellular and intracellular transport of vitamin A are facilitated by specific binding proteins but probably not in the cellular uptake of vitamin A. Subcellularly, vitamin A may exert a direct effect on transit through the Golgi apparatus, as observed from both biochemical and morphological studies. In my laboratory, recent work using cell-free systems has shown that retinol stimulates transition vesicle formation from endoplasmic reticulum in a GTP-requiring step.

Modification of transplasma membrane oxidoreduction by SV40 transformation of 3T3 cells

Transformation of 3T3 cells by SV40 virus changes the properties of the transplasma membrane electron transport activity which can be assayed by reduction of external ferric salts. After 42 h of culture and before the growth rate is maximum, the transformed cells have a much slower rate of ferric reduction. The change in activity is expressed both by change in Km and Vmax for ferricyanide reduction. The change in activity is not based on surface charge effect or on tight coupling to proton release or on intracellular NADH concentration. With transformation by SV40 virus infection the expression of transferrin receptors increases, which correlates with greater diferric transferrin stimulation of the rate of ferric ammonium citrate reduction in transformed SV40-3T3 cells than in 3T3 cells.

Chloroquine-sensitive transplasmalemma electron transport in Tetrahymena pyriformis: a hypothesis for control of parasite protozoa through transmembrane redox

Plasma membrane electron transport was studied in a protozoan cell, Tetrahymena pyriformis, by assaying transmembrane ferricyanide reduction and the reduction of iron compounds. The rates of ferricyanide reduction varied between 0.5 and 2.5 mumol/g dry wt. per min, with a pH optimum at 7.0-7.5. Other active non-permeable electron acceptors, with redox potentials from +360 to -125 mV, were cytochrome c, hexaammine ruthenium chloride, ferric-EDTA, ammonium ferric citrate, and indigo di-, tri- and tetrasulfonates. It was found that Tetrahymena cells can reduce external electron acceptors with redox potentials at pH 7.0 down to -125 mV. Ferricyanide stimulates ciliary action. Transmembrane ferricyanide reduction by Tetrahymena was not inhibited by such mitochondrial inhibitors as antimycin A, 2-n-heptyl-4-hydroxyquinoline N-oxide, or potassium cyanide, but it responded to inhibitors of glycolysis. Transmembrane ferricyanide reduction by Tetrahymena appears to involve a plasma membrane electron transport chain similar to those of other animal cells. As in other cells, the transmembrane electron transport is associated with proton release which may be involved in internal pH control. The transmembrane redox system differs from that of mammalian cells in a 20-fold greater sensitivity to chloroquine and quinacrine. The Tetrahymena ferricyanide reduction is also inhibited by chlorpromazine and suramin. Sensitivity to these drugs indicates that the transplasma membrane electron transport and associated proton pumping may be a target for drugs used against malaria, Trypanosomes and other protozoa.

Diferric transferrin reduction by K562 cells. A critical study

This paper critically examines the redox activity of K562 cells (chronic myelogenous leukemia cells) and normal peripheral blood lymphocytes (PBL). Ferricyanide reduction, diferric transferrin reduction, and ferric ion reduction were measured spectrophotometrically by following the time-dependent changes of absorbance difference characteristic for ferricyanide disappearance and for the formation of ferrous ion:chelator complexes. Bathophenanthroline disulfonate (BPS) and ferrozine (FZ) were used to detect the appearance of ferrous ions in the reaction mixtures when diferric transferrin or ferric reduction was studied. Special attention was devoted to the analysis of time-dependent absorbance changes in the presence and absence of cells under different assay conditions. It was observed and concluded that: (i) FZ was far less sensitive and more sluggish than BPS for detecting ferrous ions at concentrations commonly used for BPS; (ii) FZ, at concentrations of at least 10-times the commonly used BPS concentrations, seemed to verify the results obtained with BPS; (iii) ferricyanide reduction, diferric transferrin reduction and ferric ion reduction by both K562 cells and peripheral blood lymphocytes did not differ significantly; and (iv) earlier values published for the redox activities of different cells might be overestimated, partly because of the observation published in 1988 that diferric transferrin might have loosely bound extra iron which is easily reduced. It is suggested that the specific diferric transferrin reduction by cells might be considered as a consequence of (i) changing the steady-state equilibrium in the diferric transferrin-containing solution by addition of ferrous ion chelators which effectively raised the redox potential of the iron bound in holotransferrin, and (ii) changing the steady-state equilibrium by addition of cells which would introduce, via their large and mostly negatively charged plasma membrane surface, a new phase which would favor release and reduction of the iron in diferric transferrin by a ferric ion oxidoreductase. The reduction of ferricyanide is also much slower than activities reported for other cells which may indicate reduced plasma membrane redox activity in these cells.

Cell surface actions of adriamycin

Adriamycin has a vast range of reported actions on the structural and functional properties of cells. This review summarizes the literature on the ability of the drug to modulate the cell surface membrane and attempts to address the question of how such actions could be linked to cytotoxicity. In addition, we consider the use of polymer immobilization of adriamycin to separate intracellular from plasma membrane effects of the drug, and show how this approach has been helpful in interpreting the pharmacology of adriamycin. Finally, a range of biophysical and spectroscopic approaches to defining the molecular details of adriamycin-bilayer interactions is surveyed, and the results used to discuss a model for how this antineoplastic agent binds to membranes.

Exogenous doxorubicinol induces cardiotoxic effects in rats

An investigation was performed in the rat to assess the cardiotoxic effects of exogenous doxorubicinol compared with those induced by an equimolar dose of its parent drug doxorubicin. Rats received synthetic doxorubicinol or doxorubicin 3 mg/kg i.v. weekly for 3 weeks and were observed for a further period of 4 weeks. Survival, body growth, ECG parameters, and heart histopathology were studied. Doxorubicin markedly affected rat body growth, as well as several ECG parameters such as S alpha T, R alpha T, alpha TP and T-wave. Typical cardiac histological alterations were also induced by doxorubicin. In a similar way, doxorubicinol treatment was associated with a significant inhibition of rat body weight increase, and the appearance of ECG alterations as well as both macro- and microscopic signs of cardiac tissue damage. However these effects were delayed in time and their severity was lower compared with doxorubicin. Overall results indicate that doxorubicinol induces a doxorubicin-like toxic syndrome mainly affecting the heart, although to a lower degree of severity than that caused by the parent drug. It is suggested that the lower toxic potential displayed by doxorubicinol might be due at least in part to its greater polarity and a consequently lower cardiac tissue uptake compared with doxorubicin.

Alteration of EGF-receptor binding in human breast cancer cells by antineoplastic agents

Polypeptide growth factors bind to membrane receptors on human breast cancer cells and stimulate cell proliferation, suggesting that they may be important in growth regulation. Inhibition of the stimulatory effects of these factors might result in antineoplastic activity. Since cytotoxic drugs have been shown to alter cell membrane characteristics, we have examined the effects of a variety of antitumor drugs on the binding of epidermal growth factor (EGF) to the membrane receptor of human breast cancer cells. Twenty-four standard or investigational cytotoxic drugs were screened at a concentration of one-tenth the achievable peak plasma level for their ability to inhibit binding of 125I-EGF to its receptor in MCF-7 human breast cancer cells. Although at this concentration statistically significant inhibition of binding was observed with 11 drugs, the maximum inhibition observed was only 27%. Five agents, representing classes of drugs with different modes of action, were then studied in more detail. Of these, preincubation with 5-fluorouracil, 4-hydroperoxy-cylophosphamide and doxorubicin inhibited MCF-7 colony formation in a dose-dependent manner, but these drugs had no effect on EGF-binding even at a concentration of 10 times the peak plasma level. Preincubation of cells with vinblastine and cisplatin, however, resulted in both reduced colony survival and a parallel reduction in EGF receptor binding. Membrane integrity, as measured by trypan blue exclusion, was not altered. Scatchard analysis of EGF binding demonstrated that the major effect of cisplatin was a reduction in binding affinity. We conclude that cisplatin and vinblastine at high concentrations can inhibit the binding of EGF to human breast cancer cells offering an additional possible mechanism for their antiproliferative activity.

Changes in autorhythmic heart frequency elicited by redox agents

In isolated frog heart it was established that methylene-blue (MB, an oxidizing agent) decreased, while ascorbate (ASC, a reducing agent) increased the frequency of autorhythmic heart contractions. After MB treatment, in parallel with this phenomenon, the extracellular K+ concentration [K+]o showed a slow increase, but following ASC application a slow decrease occurred. Since these correlations are in good accordance with the idea that the pacemaking ability of heart, among other properties, depends on the voltage and time-dependent decrease in potassium conductance following the spike, changes in [K+]o might be one mechanism by which oxidizing and reducing agents modulate heart frequencies. On the basis of the effect of insulin (INS) and K-strophantoside (STR) on these modulatory influences, it is presumed that the changes in slow delta [K+]o transients might result, at least partly, from the effect of redox agents on the active transport system. In light of the increase in passive K+ fluxes after oxidant treatment and the decrease in this parameter following reductant treatment an effect of redox agents on the characteristics of the K+-channel is also postulated.

Transplasmalemma electron transport is changed in simian virus 40 transformed liver cells

Transplasma membrane electron transport activity by fetal rat liver cells (RLA209-15) infected with a temperature-sensitive strain of SV40 has been measured with cells grown at the restrictive temperature (40 degrees C) and permissive temperature (33 degrees C). The transformed cells grown at 33 degrees C had only one-half the rate of external ferricyanide reduction as the nontransformed cells held at 40 degrees C. Both the Km and Vmax for ferricyanide reduction were changed in the transformed state. The change in Vmax can be based on a decrease of NADH in the transformed cells. The change in rate with ferricyanide does not depend on change in surface charge. Reduction of external ferricyanide was accompanied by release of protons from the cells. The ratio of protons released to ferricyanide reduced was higher in the transformed cells than in the non-transformed cells. Since the transplasma membrane electron transport has been shown to stimulate cell growth under limiting serum, the changes in the plasma membrane electron transport and proton release in transformed cells may relate to modification of growth control.

Transplasmalemma electron transport from cells is part of a diferric transferrin reductase system

Intact cells are known to reduce external, impermeable electron acceptors. We now show that cells can reduce the iron in diferric transferrin at the cell surface and that this reduction reaction depends on the transferrin receptor as well as the transmembrane electron transport system. Reduction of external diferric transferrin is accompanied by oxidation of internal NADH which indicates that the transmembrane enzyme is an NADH diferric transferrin reductase. Highly purified liver plasma membranes have NADH diferric transferrin reductase activity which shows properties similar to the diferric transferrin reductases activity of intact cells. Cell growth stimulation by diferric transferrin and other impermeable oxidants which can react with the diferric transferrin reductase can be based on electron transport through he plasma membrane.

Modification of transmembrane electron transport activity in plasma membranes of simian virus 40 transformed pineal cells

Changes have been found in the plasma membrane enzyme system which carries out transmembrane electron transport and associated proton transport in Simian virus 40 (SV40) temperature-sensitive A (tsA) mutant-transformed rat pineal cell line, RPN209-1. This cell line was temperature-sensitive for the maintenance of transformation. RPN209-1 cells expressed the transformed phenotype (rapid growth, high cell density, and cloning in soft agar) at the permissive temperature (33 degrees C) and the nontransformed phenotype (slower growth, lower saturation density, and lower cloning efficiency in soft agar) at the nonpermissive temperature (40 degrees C). The reduction of external ferricyanide, hexaammine ruthenium and diferric transferrin was used to measure the transmembrane redox activity. The transformed RPN209-1 cells expressed a lower transmembrane redox activity, which is more sensitive to the antitumor drug adriamycin, when compared to the cells with a nontransformed phenotype. The lower transmembrane redox activity is associated with a decrease in the affinity for ferricyanide and a change in Vmax of the enzyme. Since the transformed cells have 25% lower concentration of NADH, the decrease in Vmax may be partly based on substrate limitation. Ionic strength variation in the assay media shows that the change in activity with transformation is not based on change in cell-surface change. Treatment with neuraminidase, however, indicates that sialic acid is important for enzyme activity, consistent with previous proposals that the transmembrane enzyme is a glycoprotein. The proton extrusion associated with transplasma membrane electron transport is increased in transformed cells relative to the rate of ferricyanide reduction. A relation between proton pumping transplasma membrane electron transport and growth stimulation by external oxidants is discussed.

Redox-dependent activation of 5'-nucleotidase in rat liver plasma membranes

Addition of NADH, but not NAD+ or NADPH, to rat liver plasma membranes resulted in the increase of their 5'-nucleotidase activity. NADH-dependent activation of 5'-nucleotidase was significantly suppressed by atebrine, an inhibitor of NADH dehydrogenase of plasma membranes, and completely abolished by 2,4-dinitrophenol (2 X 10(-4)M) and Triton X-100 (2%). Inhibitors of electron transfer in the mitochondrial respiratory chain, rotenone and potassium cyanide, failed to affect 5'-nucleotidase activity in both the presence and absence of NADH. The data obtained give reasons to suggest a redox-dependent mechanism of 5'-nucleotidase activation in rat liver plasma membranes.

Nitrogen mustard interference with potassium transport systems in Ehrlich ascites tumor cells

Nitrogen mustard (N-mustard) inhibits the ouabain-sensitive and the furosemide-sensitive Rb uptake of Ehrlich ascites tumor cells, whereas the transport, which is resistant to both inhibitors, is not affected by the alkylating agent. At N-mustard concentrations below 10 microM, the reduction in Rb uptake is predominantly due to an interference with the furosemide-sensitive system. The dose response curve for the inhibition by N-mustard of the furosemide-sensitive Rb uptake closely parallels the dose response curve for the anti-tumor activity of the alkylating drug. This is in contrast to the behaviour of the ouabain-sensitive Rb transport. The inhibition of the furosemide-sensitive Rb uptake is expressed much less in cells which are resistant to N-mustard. The recovery of the furosemide-sensitive transport system after a single exposure to N-mustard is relatively slow and characterized by an initial 4 h lag period, whereas the repair of DNA-interstrand cross-links starts immediately after removal of the drug. At mM concentrations furosemide blocks the multiplication of Ehrlich ascites tumor cells. However, lower concentrations of furosemide which cause a 50% reduction in the furosemide-sensitive Rb uptake do not interfere with cell proliferation. This is in contrast to the behaviour of N-mustard which exerts a clear-cut depression of cell growth at concentrations leading to a 50% inhibition of the furosemide-sensitive Rb transport. It is concluded, therefore, that the inhibition of the furosemide-sensitive system alone is not sufficient to explain the anti-tumor activity of the alkylating agent. The effect is discussed as part of a more extended N-mustard-induced membrane alteration which may be important for the growth inhibitory effect of the alkylating agent.

Bleomycin control of transplasma membrane redox activity and proton movement in HeLa cells

Bleomycin, tallysomycin A, tallysomycin S10b and copper-bleomycin have been tested for their capacity to inhibit the transplasma membrane electron transport and associated proton release by HeLa cells. Transplasma membrane redox activity is measured using reduction of external ferricyanide by the cells. At 75 micrograms/ml bleomycin, tallysomycin A and tallysomycin S10b gave a maximum of 65% inhibition of the ferricyanide reduction rate; half-maximum inhibition was observed at 30 micrograms/ml. The copper-bleomycin complex was slightly more effective as an inhibitor with half-maximum inhibition at 20 micrograms/ml. Survival of cells after 1 hr of drug treatment was 50% at 25 micrograms/ml for bleomycin and copper-bleomycin and at 75 micrograms/ml for tallysomycin A. Tallysomycin A and tallysomycin S10b gave 75 to 83% inhibition of ferricyanide-induced proton extrusion, respectively at 50 micrograms/ml, whereas bleomycin and copper-bleomycin appeared to be slightly less effective with 50 to 60% inhibition, respectively, at 50 micrograms/ml. In all aspects studied, which included transplasma membrane ferricyanide reduction, ferricyanide-induced proton release, and cell survival, there were significant effects by these compounds on HeLa cells in the range of 25-50 micrograms/ml.

Effects of nitrogen mustard on potassium transport systems and membrane structure of Ehrlich ascites tumor cells

By Ehrlich ascites tumor cells 86Rb+ has been shown to be a suitable tracer for K+-transport. Sixty percent of the total 86Rb-uptake into these cells is ouabain-inhibitable, 30% is sensitive to furosemide and 10% enters the cells by ouabain and furosemide-insensitive systems. N-Mustard inhibits both the ouabain-sensitive and the furosemide-inhibitable systems. The uptake which is resistant to both inhibitors is not affected by the alkylating drug. At N-mustard concentrations below 10 microM, the reduction of the Rb-uptake is predominantly due to the inhibition of the furosemide-sensitive transport. Higher concentrations are required before a significant inhibition of the ouabain-sensitive transport can be observed. The dose response curve of the furosemide-sensitive transport--not, however, of the ouabain inhibitable pump--corresponds to the dose response curve for the antiproliferative activity of N-mustard. The recovery of the furosemide-sensitive transport after a single exposure to N-mustard is relatively slow and--in contrast to the repair of DNA cross-links--is characterized by an initial 4-hr lag period. Furosemide alone does not interfere with cell multiplication. The inhibition of the transport system alone does, therefore, not explain the antitumor activity of N-mustard. The effect is discussed as a marker for membrane lesions after exposure to alkylating agents. In order to investigate the influence of N-mustard on membrane structure, membranes were labelled with diiodofluoresceiniodoacetamide. Anisotropy curves obtained from time-dependent depolarization of delayed fluorescence indicated a mustard induced immobilization of membrane constituents. Lateral diffusion of lipophilic probes was determined by following the quenching of fluorescence of pyrene by cetylpyridinium. The latter studies yielded no evidence for a change in membrane lipid fluidity. The data are interpreted as the results of cross-links of membrane proteins by the bifunctional alkylating agent.

Reduction of extracellular potassium ferricyanide by transmembrane NADH: (acceptor) oxidoreductase of human erythrocytes

Reduction of extracellular ferricyanide by intact erythrocytes proceeds by a membrane bound, NADH-dependent reaction. It is depressed by a glycolysis inhibitor and a non penetrable sulfhydryl reagent, and activated by dehydroascorbate. Dehydroascorbate activation cannot be accounted for by release of reducing equivalents from the cells. It is concluded that the observed reaction is brought about by transmembrane NADH-acceptor oxidoreductase with donor binding at the inner and acceptor binding at the outer cell surface.

Transplasma membrane redox stimulates HeLa cell growth

Impermeable ferricyanide stimulates the growth of HeLa cells in absence of fetal bovine serum or other growth factors. A series of impermeable oxidants with redox potentials down to -125 mV stimulate equivalent growth. All of these oxidants are reduced by the transplasma membrane electron transport system. Oxidants with redox potentials below -175 mV are not reduced by the transmembrane electron transport and do not stimulate growth. Insulin which stimulates growth in absence of serum also stimulates transmembrane ferricyanide reduction. Ferricyanide increases growth in presence of insulin. Antitumor drugs, which inhibit HeLa cell growth, inhibit the transplasma membrane redox system. Transplasma membrane electron transport is accompanied by proton release from HeLa cells.

Properties of a transplasma membrane electron transport system in HeLa cells

A transmembrane electron transport system has been studied in HeLa cells using an external impermeable oxidant, ferricyanide. Reduction of ferricyanide by HeLa cells shows biphasic kinetics with a rate up to 500 nmoles/min/g w.w. (wet weight) for the fast phase and half of this rate for the slow phase. The apparent Km is 0.125 mM for the fast rate and 0.24 mM for the slow rate. The rate of reduction is proportional to cell concentration. Inhibition of the rate by glycolysis inhibitors indicates the reduction is dependent on glycolysis, which contributes the cytoplasmic electron donor NADH. Ferricyanide reduction is shown to take place on the outside of cells for it is affected by external pH and agents which react with the external surface. Ferricyanide reduction is accompanied by proton release from the cells. For each mole of ferricyanide reduced, 2.3 moles of protons are released. It is, therefore, concluded that a transmembrane redox system in HeLa cells is coupled to proton gradient generation across the membrane. We propose that this redox system may be an energy source for control of membrane function in HeLa cells. The promotion of cell growth by ferricyanide (0.33-0.1 mM), which can partially replace serum as a growth factor, strongly supports this hypothesis.

Inhibition of plasma membrane NADH dehydrogenase by adriamycin and related anthracycline antibiotics

Doxorubicin (adriamycin) is cytotoxic to cells, but the biochemical basis for this effect is unknown, although intercalation with DNA has been proposed This study suggests that the cytotoxicity of this drug may be due to inhibition of the plasma membrane redox system, which is involved in the control of cellular growth. Concentrations between 10(-6) - 10(-7) M adriamycin inhibit plasma membrane redox reactions greater than 50%. AD32, a form of adriamycin which does not intercalate with DNA, but is cytotoxic, also inhibits the plasma membrane redox system. Thus, the cytotoxic effects of adriamycin, which limit its use as a drug, may be based on the inhibition of a transplasma membrane dehydrogenase involved in a plasma membrane redox system.